In a recent microwave wireless communication system, an FET capable of highly efficient operation by use of LDMOS, GaN or the like is employed, as an amplifier in a wireless communication device, such as a base station. Further, by allowing nonlinear operation at the operating point of the amplifier (class B, class C, etc.), high efficiency is achieved.
Since the amplifier has a characteristic which is varied by an operating temperature, it is preferable to maintain the operating temperature within a certain range to secure a tolerable characteristic. As a measure therefor, by the detection of the amplifier temperature, heating by a heater or cooling by a fan is performed according to the detected temperature. In particular, in regard to a base station mounted outdoors, there may be cases that the installation is made in a district beyond the range of the operating temperature of the amplifier, like in an extremely cold district of −40° C., for example. It is preferable to allow the amplifier to operate normally even when being installed in a district having such the temperature condition.
FIG. 1 is a block diagram illustrating the temperature control of the amplifier in the conventional transmission function portion of the wireless communication device. A timing controller 10 for controlling high-speed switching between transmission and reception in the TDD (Time Division Duplex) system generates a control signal for switching between transmission and reception. The control signal is supplied to a transmission switch (RFSW) 11 and a TDD switch (TDDSW) 13. The transmission switch 11 is ON during the transmission timing period, so that an RF signal is input to a transmission power amplifier (Power Amplifier: PA) 12 only during the above period. The transmission power amplifier 12 amplifies and outputs the input RF signal. During the transmission timing period, the TDD switch 13 transmits the RF signal output from the transmission power amplifier 12, and during the reception timing, the TDD switch 13 forwards a received signal to a reception function portion Rx (not illustrated in the figure).
A power supply unit (Power Supply: PS) 14 for amplifier supplies the transmission power amplifier 12 with power (current). Since the transmission power amplifier 12 is an amplifier performing nonlinear operation, the transmission power amplifier 12 consumes the current (power) supplied from the power supply unit 14 for amplifier, only in the period when the RF signals are input to the transmission power amplifier 12, and however, consumes only an idle current, which is extremely small, when there is no RF signal input. Further, a temperature detector 15 detects the temperature of the transmission power amplifier 12. When the detected temperature is lower than a threshold temperature for heater, the temperature detector 15 initiates a power supply unit 16 for temperature control. The power supply unit 16 for temperature control then supplies a heater 17 with power, so that the transmission power amplifier 12 is heated by the heater 17. Then, when the detected temperature becomes higher than the threshold temperature for heater, the power supply unit (Power Supply: PS) 16 for temperature control suspends the power supply to the heater 17. Similarly, when the detected temperature is higher than a threshold temperature for fan, the temperature detector 15 initiates the power supply unit 16 for temperature control. The power supply unit 16 for temperature control supplies a fan 18 with power, so that the transmission power amplifier 12 is cooled by the fan 18. Then, when the detected temperature becomes lower than the threshold temperature for fan, the power supply unit 16 for temperature control suspends the power supply to the fan 18.
FIGS. 2A-2C are diagrams illustrating a load variation at the time of switching over the transmission/reception timing. When the transmission and the reception are switched over at high speed in the TDD system, at the timing of switching over between the transmission and the reception [FIG. 2A], an instantaneous current variation (inrush current) occurs in the power supply unit 14 for amplifier because of the load variation caused by the inrush or the disconnection of an input signal to the transmission power amplifier 12 [FIG. 2B]. At this time, because of incapability to respond to the above variation at high speed, the power supply unit 14 for amplifier produces an instantaneous voltage variation (voltage drop) in the transmission power amplifier 12 [FIG. 2C], and as a result, may possibly produce malfunction in the operation of the transmission power amplifier 12. For this reason, by mounting a capacitor having a large capacity on a power line of the transmission power amplifier 12, it is required to suppress the variation in the bias voltage for the transmission power amplifier 12.
Now, in the patent documents 1 and 2 illustrated below, there is disclosed a technique for increasing temperature to an operating temperature by self-heating an amplifier. Also, with regard to a cooling unit for tuner, VCR, video disk recorder, or the like, having a drive unit (for an electric open/close door, a loading tray, etc), the patent document 3 illustrated below discloses a configuration to suspend the operation of a cooling fan when the drive unit is in operation. With regard to a fan motor controller for cooling the inside of an electronic apparatus, the patent document 4 illustrated below discloses a configuration to drive a plurality of cooling fans in time division.    [Patent document 1] Japanese Laid-open Patent Publication No. 2004-173055.    [Patent document 2] Japanese Laid-open Patent Publication No. 2005-348130.    [Patent document 3] Japanese Laid-open Patent Publication No. 02-251072.    [Patent document 4] Japanese Laid-open Patent Publication No. 11-202977.
In the amplifier performing nonlinear operation, when there is no signal input, current consumed in the amplifier itself is extremely small, providing no means for heat generation. Therefore, when an operating environment temperature is lower than a specified temperature required for a stable amplifier operation, it is required to heat by means of the heater 17 etc., as described above. Also, when the operating environment temperature is higher than a tolerable temperature, it is required to radiate heat by means of the fan 18.
Accordingly, it is required to provide the power supply unit 16 for temperature control to supply the heater 17 and the fan 18 with power, independently of the power supply unit 14 for amplifier. This causes an increased mounting area and an increased cost, and also necessitates extra power consumed when driving the heater 17 or the fan 18.
Further, in case of the self-heating as illustrated in the aforementioned patent documents 1 and 2, although there is a merit of no need of mounting the heater, intrinsic amplification operation cannot be performed during the self-heating (the patent document 1), and an input of a signal other than the RF signal to the amplifier is required (the patent document 2), and further, cooling operation cannot be attained at the time of high temperature.
Furthermore, in order to secure a stable TDD operation, it is required to mount a capacitor having a large capacity, as described above. In recent years, a high voltage device of GaN or the like has been adopted in the amplifier 12. This requires a high voltage-resistant capacitor, causing a difficulty in securing sufficient capacitor reliability, and also, bringing about an increased mounting area because of a larger capacitor size.